1. Field of the Invention
The present invention relates to a projector, and more particularly, to a projecting optical system.
2. Discussion of the Related Art
In recent years, projectors have become popular and various forms of projectors are manufactured. The projectors may be divided into products with light intensity applicable to a small screen and products with light intensity applicable to a large conference room or a theater. Also, projectors may be divided into projectors of a small portable size and projectors of a large size according based on purpose or use.
Display devices employed for projectors may be divided into LCD (Liquid Crystal Display) panels and DMD (Digital Micromirror Device) panels. In recent years, a plurality of projectors using the DMD panel, which is widely used, have been manufactured. The projector using the DMD panel is normally called a DLP (Digital Light Processing) panel.
A DMD panel used for a DLP projector includes a plurality of little micromirrors in a square form horizontally/vertically arranged which function as pixels. Tilting each micromirror around an axis of a diagonal line is performed by an electrical signal.
Therefore, when light is received by the DMD panel, an angle of the light reflected is changed by tilting the micromirrors. In this case, the angle of the light formed by tilting the micromirrors is not continuously changed, and the micromirrors are tilted in only two directions, such that a direction of the light is controlled using the micromirrors.
In this case, the micromirrors in the DMD panel are tilted in a diagonal direction of the micromirrors, and the light brought to incidence on the DMD panel needs to incidence in a direction at an angle of 45° to the diagonal line. The projecting optical system described below in accordance with a related art includes a TIR prism or mirror which is tilted by an electrical signal such that light brought to incidence on the TIR prism or mirror is at an angle of 45° to the diagonal line. Therefore, there is a problem in making the projector in a small size. This will be described in more detail referring to the appended drawings.
FIG. 1 is a top view of a projecting optical system in accordance with the related art. FIG. 2 illustrates a side view of a projecting optical system in accordance with the related art.
As illustrated in FIG. 1 and FIG. 2, the projecting optical system includes a lamp 101 for generating light, a color divider 102 for transmitting a particular wave of light, a illumination mixer 103 for receiving transmitted light and equally distributing the luminosity, a first illumination lens 104 and a second illumination lens 105 for controlling the luminosity, a first mirror 106 and a second mirror 107 for changing the direction of light, a TIR prism 108 for changing the angle of light to a particular angle, a DMD panel 109 for controlling light and darkness of an image by tilting the micromirrors (not illustrated), and a projecting lens 110 for receiving light reflected by the DMD panel 109 and projecting the light in a predetermined direction.
The projecting optical system composed as aforementioned in accordance with the related art will be described below. First, the lamp 101 irradiates light through a bulb that forms light and a reflective mirror that reflects light. Then, the light irradiated from the lamp 101 is divided into a plurality of colors according to time by rotation of the color divider 103 and then brought to incidence on the illumination mixer 103. In this case, the color divider 102 includes a plurality of filters for transmitting or reflecting only a particular color (red, green, blue) with the particular wave, and is rotatably provided via a motor.
The illumination mixer 103 maintains luminosity on an emission plane although luminosity of light brought to incidence on an incidence plane is not equal. Accordingly, the emission plane performs a role of a plane light source.
The light equally irradiated as aforementioned is brought to incidence on the DMD panel 109 by the first lens 104 and the second lens 105. However, the light incident on the DMD panel 109 needs to have a predetermined angle. Desirably, the light should be brought to incidence on the DMD panel 109 in a direction at 45° to the diagonal line.
To be parallel with an axis of a projecting lens 110, the angle of the light incident on the DMD panel 109 in a normal direction also needs to be at a predetermined angle. Therefore, in the structure of the illumination optical system, as illustrated in FIG. 1 and FIG. 2, the first mirror 106 and the second mirror 107 are provided between the illumination lens 104 and the second illumination lens 105. The direction of the light is changed to upward and downward for irradiating the light in a diagonal direction of the micromirror corresponding to the pixel of the DMD panel 108. As a result, the TIR prism 108 is also provided in a direction inclined by 45° to the diagonal line of the pixel for transmitting or reflecting light according to a characteristic of the incident angle of light.
Therefore, light incident on the DMD panel in a predetermined direction at a predetermined angle is inclined to an angle enabling light indent on the projecting lens 110 or in an opposite direction by the electrical signal from outside so as to create a division of light and darkness on the screen.
In the case, as illustrated in FIG. 2, there is a problem in making the projecting optical system in a small size because a channel of the light needs to be moved a large amount and the height of the projecting optical system can not be lowered for bringing the light incident on the second illumination lens 105 at a top portion of the TIR prism inclined 45°.